This invention relates to disc brakes for motor vehicles, and in particular to an improved disc brake backing plate, as well as a method of manufacturing the backing plate.
Although disc brakes have been used on motor vehicles for many years, their use has increased substantially in recent years. In particular, there has been a significantly increased use of disc brakes on lower priced cars and trucks. with a consequent interest in methods of reducing the cost of manufacturing disc brakes and replacement parts therefor on the part of both motor vehicle manufacturers and suppliers of parts for disc brakes. This increased use has also led to a significant increase in the after-market for disc brake replacement and repair.
Disc brakes, as currently manufactured, combine two main parts namely a backing plate and a friction pad. The backing plate is mounted in a brake assembly, and may be formed by stamping a suitable metal blank to produce a backing plate with a variety of bosses, holes, or other features for receiving and retaining the friction pad. The need to use high speed low cost manufacturing methods often results in irregularities in the backing plate which may lead to difficulties in attaching and/or retaining the friction pad on the backing plate during braking, when the friction pad is in contact with the rapidly turning brake rotor, or even during the pre-installation handling of the brake pad assembly.
There are a variety of known ways of attaching a friction pad to a backing plate. One such way is to attach the friction pad to the backing plates using rivets. One disadvantage of the riveting process is that it creates a rigid bond between the backing plate and the friction pad, which can, as a result of a sudden impact, lead to breaking of the friction pad. Furthermore, this process often requires one or more additional manufacturing steps with a consequent increase in cost. In addition, when the friction pad is worn down over time, the rivets become exposed and rub against the brake rotor, causing scoring on the rotor which is costly to repair.
Another, more recently developed method of mounting the friction pad on the backing plate is to use a pressurised molding process to mold the friction material directly onto the backing plate. In this process, the friction pad may be prepared by blending the components of the friction pad into a pre-form material or cake. A conventional pressurized molding system is used to mold the friction pad pre-form onto the backing plate. A layer of adhesive, such as cement or glue is often applied to the contact surface of the backing plate to improve the adhesion between the backing plate and the friction pad.
As pressure is applied to the mold assembly, the pre-form becomes heated and begins to flow, filling the mold and covering the appropriate surface of the backing plate. In this process, the pre-form material is intended to flow into and around the various features to improve the bond between the backing plate and the friction pad.
There is a need for a backing plate which provides improved shear and tensile strength in the bond between the friction pad and backing plate, compared to the strength which is provided by features, such as holes and bosses, stamped into the backing plate. Furthermore, when additional features are stamped into prior art backing plates to increase bond strength, additional manufacturing steps are required, adding to the cost.
The most common prior art features stamped into backing plates are circular holes. These holes often provide unsatisfactory results because, during the molding process, the pre-form cake does not completely fill all of the holes, which in turn, leads to deficient bonding between the backing plate and the pre-form. The incomplete hole fills can are clearly visible, and often raise quality concerns when inspected by buyers. The incomplete hole fills also have an aesthetically displeasing appearance, which can also make them less attractive to customers. Accordingly, it has become common practice in prior art backing plates to fill the incomplete hole fills with putty and to paint over them, to both hide the unsatisfactory molding results and to improve appearance. These additional manufacturing steps have the added disadvantage of increasing the cost of manufacturing the disc brake.
Another example of a prior art backing plate is disclosed in U.S. Pat. No. 5,141,083. This patent discloses retaining structures which include a ridge surrounding a depression. However, the patent does not disclose a nib surrounded by a ridge which together act to trap the friction material to provide an improved bond between the backing plate and the friction material.
The backing plate is subjected to a number of forces, such as the jarrring of the moving vehicle, as well as vibration caused by the rotor and noise. Accordingly, there is a need for a backing plate which provides improved structural strength, and is able to reduce the likelihood of premature failure.
Consequently, there is a need for a disc brake backing plate and a method of manufacturing same which can provide improved bonding with the friction pad without increasing the cost of producing the backing plate.
It is an object of the invention to provide a backing plate which provides an improved bond between it and the friction pad, thereby eliminating the need for adhesive application. In addition, it is an object of the invention to increase the structural strength of the backing plate, without increasing the cost of producing the backing plate.
According to a first aspect of the invention, a disc brake backing plate comprises a plate having at least one retaining structure defined on a first surface thereof for securing a friction material to the first surface. Each retaining structure has at least one nib surrounded by a ridge. Preferably, each retaining structure includes two diverging nibs projecting out of a circular depression formed in the first surface. The ridge preferably surrounds the depression.
According to a second aspect of the invention, a method of manufacturing the backing plate is disclosed which reduces time and cost by requiring fewer manufacturing steps, while at the same time improving the structural strength of the backing plate.
A method of manufacturing a disc brake backing plate for securing a friction material to a first surface thereof is disclosed. The method comprises the step of punching a plate to form a depression within the first surface thereof, the depression having a projection protruding outwardly therefrom. Preferably, the first surface of the plate is punched with a first punching tool to form a cylindrical projection surrounded by an amnular depression. The first punching tool preferably comprises an elongate cylindrical member having a cylindrical longitudinal channel defined therein.
Preferably, before the first step, a second surface of the plate is placed against a flat surface having a cylindrical recess defined therein. The recess preferably defines a central opening therein. The opening is preferably adapted to secure a first bushing therein. The first bushing preferably projects from the recess.
Preferably, the method comprises a second step of punching the plate to form a ridge surrounding the depression. Preferably, the first surface punched with a second punching tool to divide the projection into two nibs and to form an annular ridge surrounding the depression. The second punching tool preferably has a chisel projecting from a central recessed portion thereof. Preferably, the second punching tool has a larger diameter than the first punching tool.
Prior the second step, the second surface of the plate is preferably placed against a flat surface having a second surface opening defined therein. The second surface opening is preferably adapted to secure a second bushing therein.
Further features of the invention will be described or will become apparent in the course of the following detailed description.